Burnham C, Braw R, Karlish S J
J Membr Biol. 1986;93(2):177-86. doi: 10.1007/BF01870809.
This paper describes properties of 86Rb fluxes through K channels in "luminal" membrane vesicles prepared from rabbit renal outer medulla. By measuring 86Rb uptake against an opposing chemical gradient of K ions, using membranes loaded with KCl, a transient accumulation of isotope is observed, which is blocked by Ba ions. This is the behavior expected of a conductive Rb flux through a Ba-sensitive K channel. The 86Rb accumulation is driven by an electrical diffusion potential as shown in experiments using either vesicles loaded with different anions, or an outwardly directed Li gradient with a Li ionophore. The vesicles containing the channel show a cation selectivity with the order Rb greater than K greater than Cs greater than Li greater than Na greater than choline. The Ba-sensitive Rb flux is dependent on Ca within the vesicles, with a very high affinity estimated as K0.5 10 to 100 nM. The vesicles appear to be right-side-out. The Ba-sensitive 86Rb uptake is also inhibited by quinine K0.5 30 microM but is insensitive to tetraethyl ammonium ions and apamin. These isotope flux experiments complement electrophysiological experiments in providing independent evidence for the existence of K channels in the luminal surface of cells of this ascending limb of the loop of Henle. The very high Ca affinity suggests that cytoplasmic Ca could play an important role in regulation of transepithelial salt flux in this region of the nephron.
本文描述了从兔肾外髓制备的“管腔”膜囊泡中通过钾通道的⁸⁶Rb通量的特性。通过使用装载有KCl的膜，测量⁸⁶Rb逆着K离子的反向化学梯度的摄取，观察到同位素的瞬时积累，该积累被Ba离子阻断。这是通过Ba敏感的K通道的传导性Rb通量所预期的行为。如使用装载不同阴离子的囊泡或带有Li离子载体的外向Li梯度的实验所示，⁸⁶Rb积累由电扩散电位驱动。含有该通道的囊泡表现出阳离子选择性，顺序为Rb＞K＞Cs＞Li＞Na＞胆碱。对Ba敏感的Rb通量取决于囊泡内的Ca，估计其亲和力非常高，K₀.₅为10至100 nM。这些囊泡似乎是外翻的。对Ba敏感的⁸⁶Rb摄取也被奎宁（K₀.₅为30 μM）抑制，但对四乙铵离子和蜂毒明肽不敏感。这些同位素通量实验补充了电生理实验，为Henle袢升支细胞管腔表面存在K通道提供了独立证据。非常高的Ca亲和力表明细胞质Ca可能在该肾单位区域的跨上皮盐通量调节中起重要作用。
